"Night-Shining" Clouds Bring Mystery

"Night-shining" clouds bring mystery

Since their discovery 120 years ago, strangely luminescent clouds called noctilucent clouds have been creeping slowly toward the equator.

Once confined to Earth's poles, the bizarre clouds have now been spotted above central Colorado, and they appear to be getting brighter and more numerous, too, said David Rusch, a University of Colorado atmospheric scientist.

This month, NASA plans to launch the $110 million AIM (Aeronomy of Ice in the Mesosphere) mission to measure noctilucent clouds and the circumstances in which they form - which may be linked to climate change.

The satellite will measure air temperature and pressure, moisture content and cloud dimensions.

Researchers at the University

of Colorado at Boulder will control the satellite, process data and try to understand what some call the planet's most mysterious clouds.

Noctilucent clouds appear only at night, when their altitude - 50 miles up in the atmosphere - lets them catch sunlight no longer visible from Earth's surface, said James Russell, an atmospheric scientist at Hampton University in Virginia, the NASA mission's principal investigator.

That makes noctilucent - "night-shining" - clouds appear almost iridescent, he said. Most normal clouds are less than 10 miles up.

"They're very beautiful, they look very mysterious, but aside from all that, these clouds are changing in ways we don't understand," Russell said.

Researchers have many ideas about why noctilucent clouds may be growing in number and brightness, and most of them are related to global warming.